At this point, it would be a good idea to mark all AC_FUNC_* macros that
request an AC_LIBOBJ replacement as obsolete and refer the user to Gnulib
for both the macro and the workaround code (and the documentation).
Except maybe AC_FUNC_MALLOC and AC_FUNC_REALLOC, because the replacement
code for them is so trivial that anyone can make it up himself.